1. Field of the Invention
This disclosure relates to a medium conveyance device and an image formation apparatus.
2. Description of Related Art
Conventionally, an image formation apparatus, such as a printer (used as an example herein), a copier, a facsimile machine, or a multi-purpose machine includes an image formation unit, an LED head, a transfer roller, a fixation device, a sheet cassette, and the like. The image formation unit has a photosensitive drum, a charge roller, a development roller, a development blade, a toner supply roller, a cleaning blade, a toner cartridge, and the like. Toner is contained in the toner cartridge, and sheets are contained in the sheet cassette.
In the image formation unit, the surface of the photosensitive drum is uniformly charged by the charge roller and is exposed to light by the LED head, and thereby an electrostatic latent image is formed on the photosensitive drum. Then, the toner supply roller supplies the development roller with toner supplied from the toner cartridge to a main body of the image formation unit, and the toner on the development roller is formed into a thin film by the development blade. Then, the toner on the development roller is attached to the electrostatic latent image on the photosensitive drum, thereby developing the electrostatic latent image and forming a toner image on the photosensitive drum.
A sheet picked up from the sheet cassette is separated one by one by a pair of sheet-feed rollers and is corrected for its skew. Thereafter, the sheet is fed to a transfer area between the photosensitive drum and the transfer roller, and the transfer roller transfers the toner image onto the sheet.
Then, the sheet having the toner image transferred thereon is fed to the fixation device which fixes the toner image to the sheet, and thus, an image is formed. The sheet having the image formed thereon is ejected to the outside of the main body of the printer, i.e., outside of the apparatus main body.
To correct the skew of a sheet picked up from the sheet cassette, a roller conveyance mechanism (a medium conveyance device) is provided on a sheet conveyance route. This roller conveyance mechanism includes components such as a registration-roller pair including a registration roller (a first roller) and a pressure roller (a second roller) provided facing the registration roller (see, for example, Japanese Patent Application Publication No. 2004-83203).